Hermit crab does not have bones. Its body consists of body tissue, which is protected by the exoskeleton. Here comes the main part, because this exoskeleton does not grow. Therefore, the only way a crab can grow is to shed it periodically. This process we call Molting.
Molting is how a Hermit crab physically grows. When a Hermit crab molts it sheds the exoskeleton. That is all the hard skin on the legs and claws. Do not confuse it with changing shells.
When they molt they are soft and vulnerable. That is why you should not touch them while their exoskeletons are still soft. Keep in mind, that even in nature almost 90 % of invertebrate deaths are related to molting. So, do not reduce their chances of survival.
Molting Process and Stress Behavior
First of all, I would like to start off by saying that sometimes people also confuse the molting and stress behavior of the Hermit crabs. They believe, that losing limbs means molting. Well, it is not! Losing limbs has absolutely nothing to do with molting. Molting is the shedding and regrowth of the exoskeleton. If your Hermit crabs are losing their legs. It means incorrect temperature, humidity, environment, or post-purchase syndrome.
The molting process (the molt cycle) is the most important part of the Hermit crab’s life. If you think that it only happens with crabs from time to time and takes a few weeks, you are wrong. This process has 4 phases: inter-molt, pre-molt, molt, and post-molt. As a result, they spend most of their time (80 – 90%) getting ready to molt, molting, or recovering from a molt.
Note: Some time ago, I wrote an article about “Aquarium: Molting Process and Metabolism of the Dwarf Shrimp”. Like shrimp, Hermit crabs follow the same rules and principles. Check it out if you are interested.
Signs of Incoming Molting (Pre-molt Phase)
At this stage, the old exoskeleton begins to detach from the skin, and the new exoskeleton begins to form below. There are some signs that your Hermit crab is going to molt.
1. Difference in behavior
Every Hermit crab has a personality. They prefer to eat a certain amount of food. They play or sleep a certain amount of time. In general, they act a certain way. So, when they are about to molt their behavior will change. For example:
Your Hermit crab will eat a lot. Then for a few days before molting, they seem to stop eating and get very lethargic and lazy.
- Changing Shells
All of a sudden, your Hermit crab becomes uncomfortable with the shell it is wearing. It starts changing shells more often compared to normal behavior. In many cases, they prefer moving even into a smaller shell. People believe that with small shells it is easier for them to bury themselves.
- Substrate Testing
They may be trialing the substrate by digging holes in different places. They might just keep burying themselves coming up, burying themselves coming up, again and again. It seems like they are trying to find the best spot.
- Lethargic Behavior
They move less. Sometimes they start dragging their large claw almost under them as if it is too heavy.
- Water Preferences
Hermit crabs start spending more time near the water ponds.
2.Difference in appearance
- Cloudy eyes
Another molting sign is brownish eyes. Usually, your Hermit crab’s eyes are perfectly black and shiny. Cloudy eyes are a sign of an impending molt.
- The color of the exoskeleton
You will notice that the color of your Hermit crab looks a little bit dimmer or duller.
3. Fat pouch developing
One very interesting and very common molting sign is a fat pouch developing on the Hermit crab. You can see it inside the shell, on the right of the abdomen. It will get larger. Hermit crabs develop these fat pouches so that while they are buried they have some food so they do not starve.
4. Limb regeneration
If your Hermit crab does not have a limb, it will begin the process of regenerating it. At first, it looks like a small nub. However, as the time for molting grows near, it will swell and become more defined.
Note: Keep in mind that all of these signs not always occur and sometimes none of them do.
Types of Molting (Molting Phase)
During the molting phase, the old exoskeleton cracks, and the Hermit crab pulls out of it backward. While the tissues are still soft, they start increasing their size by using water, which they carry in their shell and the body. They create water pressure to stretch the new soft exoskeleton into a larger size.
Hermit crabs have only 2 ways of molting.
1. Underground Molting (safe and stress-free)
2. Surface molting (unsafe, when they are seriously stressed or sick)
Hermit Crabs and Underground Molting
When Hermit crabs are going to molt they will usually bury themselves entirely. They need depth, darkness, moisture, and heat to successfully molt. Thus, the most important that you can do – DO NOT dig it up.
Digging up a molting Hermit crab can lead to death. In nature, they do not need your help. Do not kill with kindness. When they buried just leave them alone.
Note: Normally Hermit crabs handle molts all on their own without many problems. The main danger is that in captivity, they are kept in a much smaller space and so are more likely to discover each other when they dig around. This is one of the reasons why you should not keep them in small tanks. This is why your tank should have at least 3 inches (absolute minimum!) of the substrate along the bottom so they could bury.
Hermit Crabs and Surface molting
Surface molting is when a crab molts without burying itself. As I have just said, Hermit crabs usually molt underground. They will molt above ground only when they cannot bury themselves because of the substrate (unsuitable or not deep enough) or physical conditions (stress, illness, etc).
Do not try to bury Hermit crab yourself. You will make it only worse. During molting, they do not have the strength to create a new tunnel or cave underground. As a result, it can kill them.
However, you still can help your Hermit crab:
- Make the substrate around molting Hermit crab soft and leave it on the surface of it.
- Put any pieces of exoskeleton you found and (or) any other soft food that is easy to eat.
- Cover the tank with a dark blanket, too to make them less stressed.
Important: If a crab has a surface molt you need to move all your other Hermit crabs away or they will eat it during the molting.
Isolation During Molting
One of the most important things you need to do when your Hermit crab is going to molt is to isolate it. This is the only way you can be sure that it will be safe from other crabs. The problem is that in this phase, molting crabs are soft, weak, and cannot fight back. Easy prey. In the wild, it happens pretty commonly actually.
Make sure to isolate your crab if you can. There are 3 ways to do that:
- Set up an isolation tank (ISO tank).
ISO tank should mimic your large tank (just smaller). It must have all the same stuff, a very deep substrate, pools of water, food, heaters, etc. You are only going to be putting one crab in there at the time.
- Divide your tank.
If you have a large tank and molting place allows it (for example, it is near the corner). You can section off part of the tank so the other crabs cannot reach the molding crab.
- Soda-bottle technique
Take a large soda bottle. Cut it in half. Rinse it out thoroughly. Make sure there is no soda left in there. Use the upper half the one with the opening where the cap would be and you sink it into your substrate around your molting crab. This is an easy and safe way to isolate your Hermit crab.
Soda-bottle Technique Details
If you decide to use the soda-bottle technique, there are a few specific things you should know.
1. Use it only in the first few days when they buried.
When Hermit crabs bury to molt they make a little underground cave. The main idea of using the soda-bottle is to cover both your crab and their lair. Therefore, if you miss, you may collapse their cave. It will not be a big problem for a crab who has only been buried a few days. It is very likely it has not molted yet. So, even if you do accidentally destroy the cave, it will be strong enough to either rebuild it or dig a new one elsewhere. However, this would be very dangerous for a crab that has already molted. It will not be strong enough to do anything. So, it can die there.
2. This method only really works for small Larger crabs and their caves just do not fit into the soda bottle.
3. If you have a big tank with a deep substrate (6 inches or 18 cm) and you have not had problems with crabs digging each other up. You may not need to use the bottle. After all, the best way to avoid cannibalism is to give your Hermit crabs plenty of substrate, space, and provide plenty of rich, high-protein, and calcium.
Hermit Crabs and Post-molt Phase
When your Hermit crab comes up from the molt you will notice a few differences about it.
- Usually, their exoskeleton (their claws and legs) are a much lighter color once they have resurfaced after a mol It appears pale for a few days before it fully re-hardens. Next, you notice that they are very brightly colored.
- They have very long antennae.
- Hermit crabs will have “hairy” legs (tiny black spikes). Usually, in nature, these spikes break off pretty easily but recently molted crab will have them yet (regrown them).
- Hermit crabs become more active and move around a lot.
- If your Hermit crab was missing any limbs before it went under for a molt, they will grew them back. Like all invertebrates, they can regenerate any of their limbs including their big claw.
Note: If they are regenerating an entire limb it might take a few months for it to actually fully grow. For example, at first, a leg or claw will be kind of thinner or smaller. In a few months should return to normal size.
Hermit Crab and Post-molt Bathing
It is very important that after your hermit crab comes up from its molt you bath it. You can just use regular freshwater like the kind you would use in their tank to do this.
The reason behind bathing is that they do not smell like their old exoskeleton. Unfortunately, in the wild, it is a delicious smell to other crabs. Of course, you do not want them to smell delicious because then they will be attacked. Therefore, bathing your Hermit crab is necessary. Always make sure to bathe your crabs after they molt.
Frequently Asked Questions About Hermit Crabs Molting
Is Hermit crab dead or molting?
When Hermit crab passes away, you will know it without a doubt. The stench is unbearable. It almost smells like dead fish. Therefore, if you do not smell anything, your hermit crabs could be molting or just buried.
Note: If you pick up its shell and the body falls out, it is dead.
Why Should I Isolate Molting Crab?
You should isolate all of your molting crabs separately. There is the possibility of cannibalism if they are together. If they are all molting successfully in your habitat then that means, you are doing a good job.
How do you make sure that the soda bottle is covering the Hermit crab?
Really, how do you know where they bury themselves with the soda-bottle technique?
Often Hermit crabs dig to the bottom of the tank. So, you can find them by looking underneath through the glass on the bottom of the tank. If you cannot find your crab, in this case, I would not worry about it. It is more likely you will cause harm by digging it up than it is likely another crab will find it.
How long does it Take Hermit Crabs to Molt?
It depends! The amount of time it takes a Hermit crab to molt is largely determined by the size of the crab. The smaller the crab the less time it takes to molt. Therefore, the larger the crab the more time it takes the crab to molt. A small Hermit crab can take as little as 2 weeks to molt. For bigger Hermit crabs, it can take somewhere around 1 – 2 months.
Keep in mind that sometimes they will be buried for weeks without shedding, while others will bury and shed immediately. There is no real way to predict it.
Of course, it is hard to just sit and wait for a couple of weeks or months while your Hermit crab is under molting. Nonetheless, you have to understand is that this is a very stressful time for your Hermit crab. If you disturb your crab while it is molting you may seriously endanger it.
How often do Hermit Crab Molt?
It depends on the size of your Hermit crab and its environment. Smaller crabs (golf-ball sized and smaller) usually molt 2 – 4 times a year. Bigger crabs molt less frequently. As long as you are providing a good environment and a variety of food, your crabs will molt regularly.
Is Hermit Crab just digging or going to Molt?
Hermit crab keepers often ask, how do you know if your crab is molting or what if it is just digging?
Hermit crabs dig to molt, but they also dig to explore. Occasionally a crab will prefer to be underground during the day but come up at night. However, when they bury themselves and stay underground for over 24 hours, then you know they are probably molting or going to. A molting crab will stay underground in one spot for a long time. Some crabs do just dig for fun, but if the crab is staying underground he is probably going to molt.
Should I keep the food in the tank when my crab is molting?
Absolutely, yes. They can come up from the molt during night time and they will be very hungry. Give them something that is rich in calcium, like Cuttlefish bones (link to check the price on Amazon), etc. They definitely need calcium after the molt.
How deep my substrate should be?
Many Hermit crabs dig to the glass bottom of the tank. This may be a sign the substrate is not deep enough (3 inches is an absolute minimum). However, it is better to have around 6 inches of substrate. Ultimately, as long as the crab is completely buried, it should be able to successfully molt.
Molting is a very delicate and complex process for Hermit crabs. You want to make sure to have everything set up properly so your hermit crabs can mold safely.
Do not disturb them, be patient and your Hermit crab will be OK.
- Hermit Crabs – Detailed Guide: Care, Diet, and Breeding
- Hermit Crab Tank Setup
- Hermit Crab Diet
- Hermit Crab Shells: What You Need to Know
- My Hermit Crab Has Left Its Shell
- Is Hermit Crab Dead or Molting?
- How long do Hermit Crabs live? Lifespan | Life expectancy
- Mistakes That Can Kill Your Hermit Crab